Looking for a part # or name Lennox LF24

I have a Lennox LF24 heater that I am trying to install. The adapter on the back of the induce draft blower that makes it 3" for the vent pipe is missing. I need to replace this or come up with something different.

Anyone know what this part is called or a part number? The opening is just under 2 1/4" Took this pic at Lowes from another brand heater that they had on the shelf. I tried calling a couple of local places to get the part, but they will not talk to me unless they come onsite and charge me a $99 diag fee.

Looking for a part # or name Lennox LF24

Try cozyparts.com. They sell Lennox parts to the general public and can look up the part number for you. Flue gas on the heater is way too hot for anything except metal.

Thank you very much for the reply. I have a question. My furnace downstairs is vented with pvc and one side has a rubber joint. Do they work differently then the Lennox LF24 I am trying to get hooked up? Here is a pic of my furnace. Cozy quoted 43.99 for the part (2" to 3" Flue adapter) which seems high but I don't know. Just want to be sure before I spend that kind of money if it can be done differently.